LVD is a heart condition wherein the left ventricle exhibits decreased functionality. Diagnostic measurements indicative of LVD include a diminished ejection fraction and a depressed level of motility of the left ventricular wall. Hence, the ability of the stroke volume of the heart to respond to exercise is limited and a degenerative reduction in cardiac output occurs. With LVD, the heart typically attempts to increase cardiac output primarily with an increase in heart rate. Patients with LVD have an increased risk for thromboembolic events, with a significant percentage of these patients dying from such events. LVD can also lead to congestive heart failure or myocardial infarction, among other cardiovascular diseases.
Accordingly, it would be highly desirable to provide a reliable technique for detecting the onset of LVD within patients and for tracking its progression. Many patients who are significantly at risk of LVD have already had a pacemaker or implantable cardioverter defibrillator (ICD) implanted for other reasons and so it would be beneficial to configure such implantable devices to detect and track the progression of LVD as well.
One technique proposed for detecting LVD using a pacing system is set forth in U.S. Pat. No. 6,129,744 to Boute. Briefly, sensed cardiac signals are utilized to evaluate LVD. In one example described therein, changes in the rest heart rate of the patient are monitored to detect trends indicating possible LVD. When LVD is indicated, the pacing system responds by altering the pacing rate in an attempt to be more responsive to patient exercise, initiating 3- or 4-chamber pacing or administering drug therapy.
Insofar as the detection of the rest heart rate is concerned, however, the technique described by Boute does not directly determine the rest rate but instead attempts to approximate the rest rate by extrapolating from trend curves or by determining the minimum rate of a twenty-four hour period. Hence, the technique of Boute may not properly determine the true rest rate and any conclusions drawn regarding LVD from the approximated rest rates may be inaccurate or erroneous, possible triggering an improper change in pacing rate, an improper switch to a different pacing mode or the improper administration of drug therapy.
Accordingly, it would be desirable to provide an improved technique for detecting and tracking LVD using a pacing system or other implantable cardiac stimulation device, which more accurately and reliably detects the true rest rate, and it is to this end that aspects of the invention are drawn.
Once LVD is detected, drug therapy is typically administered, often using beta-blockers, angiotensin-converting enzyme inhibitors (ACEIs), diuretics, diltiazem, diltiazem, or angiotensin II antagonists. It would also be desirable to provide a technique for automatically evaluating the efficacy of such therapy using an implantable cardiac stimulation device and it is to this end that other aspects of the invention are drawn. It would also be desirable provide improved non-drug therapy for responding to LVD and further aspects of the invention are drawn to such therapy.
In circumstances where the implantable device may not have sufficient resources to perform full LVD tracking or full LVD drug efficacy evaluation, it would be desirable to instead configure the implantable device to transmit raw data to an external programmer configured to analyze the data and evaluate LVD progression and LVD drug efficacy. It is to this end that still further aspects of the invention are drawn.